The spray gun is a tool commonly used in industry, for instance, it may be used to spray paint to surfaces of various articles such as furniture, machines and particularly vehicles, respectively auto bodies. The spray gun can comprise a cup for receiving the paint material and a gun body for spraying the paint material. The paint cup can be arranged on the upper side, on the lower side or laterally of the spray gun. When the paint cup is arranged on the upper side, the spray gun is called gravity fed, when the cup is on the lower side, it's a suction or pressure fed spray gun and when the spray gun has a lateral cup it's called a side cup spray gun. As an alternative to the cup, the spray gun may comprise a hose connected with a pressure tank or a pump which supplies the spray gun with paint under pressure.
A gravity fed spray gun according to the state of the art is shown in FIG. 1 in sectional view. The spray gun 1 comprises a gun body 2, which includes a handle 21 and an upper gun body 22 with spray gun head 23. Wherein, the spray gun head 23 is connected with an air cap 5. The spray gun is supplied with compressed air via an air connection 3. The spray gun 1 has a cup connection 4, to which a paint cup can be connected. The paint cup contains the paint that is to be sprayed with the spray gun. The paint flows from the paint cup through the paint inlet 41 into the paint channel 42. The paint nozzle 26 of the gun body 2 is sealed by the paint needle 10, whereby the paint cannot leave the spray gun. When the trigger 11 is actuated, the air piston head 13, which seals the air supply 9 against the air channels inside the spray gun body, is moved backwards and away from its seat. By that, the compressed air can flow through the inner air channels to the air nozzle 55 of the air cap 5, which is a circular orifice that surrounds the paint nozzle 26. The compressed air is blown out of the air nozzle 55 under pressure.
When the trigger 11 is pressed in excess of a certain point, also the paint needle 10 is moved backwards, leaves its seat in the paint nozzle 26 and the paint nozzle 26 is opened. The paint in the paint channel 42 can flow out of the paint nozzle 26. The compressed air that is blown out of the air nozzle 55 generates a vacuum that sucks the paint out of the paint nozzle 26. Additionally, the paint is pressed out of the nozzle by the following paint. The paint flows in direction of the nozzle because of gravity in the case that the spray gun is gravity fed or because of low=pressure when the spray gun is suction fed or because of pressure when the spray gun is pressure fed or when it's supplied with paint from a paint tank via a hose. When the paint flows out of the paint nozzle 55, the paint is atomized and blown into front direction. Here, a substantially cone shaped round spray is generated.
However, for many paint and finishing works, a flat spray is preferred, because a bigger surface can be painted in a shorter time. Moreover, a more uniform and more efficient coating is possible. Thus, most air caps 5 have two lateral horns 53, particularly on the air nozzle, which protrude in direction of the paint spray. These two horns 53 are also supplied with compressed air. The compressed air is set free through one or more horn air nozzles 531 in each horn. In most cases, the nozzles 531 are circular cylindrical bores, but they can also have another shape. Many spray guns have two horn nozzles with different diameters in each horn. The horn air is directed to the paint spray and deforms it from both sides. By that, the paint spray becomes flat. Its cross section becomes smaller in the direction from that the horn air is exposed and bigger in the other both directions, thus a flat spray is formed. The air cap 5 is rotatable around the spray axis. By that, the angle of the flat spray in relation to the spray guns can be changed. In most cases, a vertical spray is desired.
FIG. 2 and FIG. 3 respective show a sectional view of the air cap arrangement and the spray gun head according to the state of the art above. Wherein, the content shown in FIG. 3 is the same as that shown in FIG. 1, but in FIG. 2, the paint nozzle 26, the paint needle 10 and a sealing in the paint inlet 41 are omitted for easier explanation.
The spray gun head consists of a spray gun body head 23 and an air cap arrangement composed of the air cap 5, a cap ring 6 and a retaining ring 7. The air cap 5 comprises two air horns 53 each having one air horn nozzle 531. The air cap ring 6 surrounds the circumferential outside surface of the air cap 5, and is connected with the gun body 2. A step 51 is arranged on the circumferential outside surface of the air cap 5 in which the outer diameter of the step 51 is larger than the outer diameter of the circumferential outside surface of the air cap 5 such that the step 51 protrudes in the radial direction and acts as a stopper for the air cap 5. A protrusion 61 is arranged on the circumferential inner surface of the air cap ring 6 and contacts against a surface of the step 51 towards the front, to prevent the air cap 5 from moving forward with respect to the air cap ring 6. And a groove 52 is also arranged on the circumferential outside surface of the air cap 5, thus through setting the retaining ring 7 in to the groove 52, the situation that the air cap 5 slips backwards and out of the air cap ring 6 can be avoided. Therefore, the step 51 of the air cap 5, the protrusion 61 of the air cap ring 6 and the retaining ring 7 ensure the connection of the air cap 5 and the spray gun head 23, and the air cap 5 is not or hardly moveable along the spray axis. The step 51, the groove 52 and the protrusion 61 are advantageously run over the whole circumference of the air cap 5 or the air cap ring 6 respectively; the retaining ring 7 is advantageously cut at one position.
However, there are still some problems in such connection manner of the air cap 5 and the spray gun head 23:
1) Since the retaining ring 7 is provided out of the cap ring 6, foreign matter such as the paint may be attached on the retaining ring 7 or near the retaining ring 7 such that it is difficult to keep the spray gun clean.
2) It is very difficult and hard for the user to remove the air cap 5 from the air cap arrangement, particularly from the air cap ring 6 for cleaning and maintenance, because the retaining ring 7 is sitting in the groove 52 of the air cap 5 very tightly and at least one tool is required for that purpose to pull or push the retaining ring 7 out of the groove 52.
3) As the retaining ring 7 is lying at the air cap 5 in front of the air cap ring 6, the air cap 5 has to be relatively long, i.e. it has to protrude out from the air cap ring 6 relatively far. By that, much material is required for manufacturing the air cap 5 and the air cap 5 becomes heavier.
4) Since the retaining ring 7 is provided out of the cap ring 1, the gun is not aesthetically pleasing.
Furthermore, as shown in FIG. 3, a circular protrusion 54, which surrounds the spray axis, is arranged on the rear surface of the air cap 5, and the outside surface of end of the circular protrusion 54 is formed as a circular cone shape 541. Furthermore, a circular protrusion 27 is also arranged on the paint nozzle 26, and the inner surface of the end of the protrusion 27 is also configured as circular cone 271. The air cap 5 can be aligned with respect to the paint nozzle 26 through making the circular cone 541 of the circular protrusion 54 to contact against the circular cone 271 of the circular protrusion 27. However, the connection manner of the air cap 5 and the spray gun head 23 limits the movement of the air cap 5, and impedes the air cap 5 from aligning with the paint nozzle 26.